1. Field of the Invention
This invention relates to regenerative fuel cells and particularly to a combined fuel cell and electrolysis cell unit.
2. Description of the Prior Art
Regenerative fuel cells are known in the art. One type of regenerative fuel cell known utilizes the same electrodes for the fuel cell during one mode of operation and for the electrolysis cell during the regeneration mode. While it is possible to perform both power generation and electrolysis with a single cell operating in a fuel cell mode at one time and in an electrolysis cell mode at another time, it is not advantageous to do so. Separating the fuel cell from the electrolysis cell permits independent optimization of the materials and configurations of each cell. Performance and durability are not as good if one cell is required to function in both modes. For example, fuel cell oxygen electrodes using a platinum catalyst have demonstrated excellent endurance and performance. However, if this type of electrode is used to evolve oxygen in an electrolysis cell, the high operating potential results in the formation of platinum oxide which reacts with the electrolyte to form soluble Pt O.sup.=.sub.3 ions. Subsequent operation of this electrode in the fuel cell mode causes these ions to migrate to the hydrogen electrode where they are chemically reduced to platinum metal which forms platinum dendrites on the hydrogen electrode. This catalyst migration eventually causes low performance, and the platinum dendrites may cause gas evolution in the electrolyte cavity and subsequent failure of the cell.
Another type of regenerative cell known in the art physically separates the fuel cell from the electrolysis cell. This configuration requires ancillary equipment such as pressure vessels, valves, pumps, controls and interconnecting plumbing to accomplish storage and transfer of water and reactant gases, which makes the system less reliable, costly, and reduces the net electrical power of the fuel cell since some of the electrical energy generated by the fuel cell must be used to power the ancillary equipment.
Our invention obviates the disadvantages and drawbacks of the above-mentioned two types of regenerative fuel cells.